U.S. Pat. No. 3,994,121 (Adams) discloses a process for making filaments of poly(hexamethylene adipamide) having a birefringence of at least 0.040 by withdrawing the filaments from the spinneret at a high spinning speed and conditioning the freshly cooled filaments with steam to increase their thermal shrinkage and to improve their package-forming characteristics prior to being wound up. The acid dyeability of filaments spun in this manner can be quite sensitive to the steaming conditions. Consequently, when steaming conditions change, such as in order to provide a desired draw-tension, boil-off shrinkage, or improved package formation, the acid dyeability of the filaments also can change resulting in a need to segregate products where dye mergeability is critical. In general, as the degree of steaming is increased, the acid dyeability of the filaments increases.
U.S. Pat. No. 4,181,697 (Koschinek et al.) teaches a similar high-speed spinning process wherein the filaments are heat-treated under specified conditions in a steamless spinning duct prior to being wound. Such a process provides for no control of acid-dyeability independently of the heating conditions required for other yarn properties such as package stability.
Partially oriented polyamide yarns made by either of the above processes are especially useful as draw-texturing feed yarns in the trade. Improvements in draw-texturing apparatuses are continually being made to permit them to operate at higher speeds which provide economies in overhead and operating expenses. Consequently, there is an accompanying demand for improved yarns which operate satisfactorily at these higher processing speeds in order to take advantage of the apparatus improvements. Important in this regard are uniformity improvements in yarn drawing tension and package formation, especially with regard to larger packages, while maintaining a uniform dyeability.
Consequently, an object of this invention is a process which facilitates the uniform preparation of partially-oriented draw-texturing polyamide feed yarns within predetermined limits of yarn properties such as draw-tension and packageability independently of acid dyeability.